An rfid based arrangement for reducing wifi handoff latency

ABSTRACT

A radio frequency identification (RFID) reader is contained in a mobile station. The RFID reader includes a transmitter for transmitting an interrogating radio frequency (RF) signal. It includes a receiver for receiving responding RF signals generated in corresponding pairs of RFID tags. Each responding RF signal contains information identifying a corresponding access point (AP). The RFID tag pairs are attached to corresponding regions of each location of corresponding locations. A processor of the RFID reader selects a responding RF signal based on signal strength and derives the information contained in the selected responding RF signal that identifies a corresponding AP among several access points that is the most appropriate one to associate with in a handoff operation.

This application claims priority to European Patent Applicationentitled, SYSTEM FOR IDENTIFYING A LOCATION OF A MOBILE TAG READER, NO.EP14306895.5, filed on Nov. 26, 2014 and forms a continuation in part(CIP) of a corresponding to-be-filed United States Patent Application(PF140319-US-PCT.)

FIELD OF THE INVENTION

The present invention is directed to a radio frequency identification(RFID) tag system for reducing handoff delay in a wireless network and,in particular, for example, local area wireless computer networking(WiFi).

BACKGROUND

In the IEEE 802.11 standard, Extended Service Set (ESS) refers to two ormore Basic Service Sets (BSS) whose respective Access Points (AP)communicate through a wired network, named Distribution System (DS). TheBSS includes an AP antenna (ant). Its associated mobile stationscommunicate in the unlicensed Industrial Scientific and Medical (ISM)radio bands. When a mobile station (MS) moves beyond the radio range ofan AP, and enters into a radio range of another BSS, the MS triggers aHandhoff process which can take from 200 ms and up to 1000 ms. Such alarge delay range may be undesirable for delay sensitive applications,such as Voice over Internet Protocol (VoIP). VoIP is a methodology andgroup of technologies for the delivery of voice communications andmultimedia sessions over Internet Protocol (IP). For the purpose of VoIPthe recommended maximum end-to-end latency is 150 ms.

In the IEEE 802.11 standard, the MS initiates the handoff process whenthe received signal strength and the signal-to-noise-ratio havedecreased significantly. The MS can either passively or actively scanfor new AP's to associate next. In the case of a fast active scan whichis faster than a passive scan, the MS broadcasts probe frames and waitsfor responses for a minimum channel time (Tmin), and continues scanninguntil a maximum channel time (Tmax) has elapsed, if at least oneresponse has been received within Tmin. Thus, the time to probe (Tprobe)n channels is given by: n*Tmin≤Tprobe≤n*Tmax. This information isprocessed by the MS to decide which BSS to join next. In general, Tprobeconstitutes 90% of the handoff delay. It may be desirable to reduce thehandoff latency. An article, Published in Wireless Communications andNetworking Conference (WCNC), 2010 IEEE, entitled, Handoff Managementrelying on RFID Technology, in the names of Apostolia Papapostolou andHakima Chaouchi proposes to predict the next point of attachment (PoA)of an RFID-enabled MS by using topology information provided by thenetwork with the collaboration of an RFID system.

The use of an RFID reader is also described in, for example, a publishedpatent application No. WO 2005/071597. There, an RFID tag array-based“smart floor” system for navigation and location determination forguiding individuals includes a plurality of spaced apart RFID tags. EachRFID tag has memory having information stored therein includingpositional information and attributes of objects or structures disposedin proximity to the tags. The tags convey radio frequency (RF) signalsincluding the positional information and the attributes in response toreceived electromagnetic excitation fields.

Long range RFID tag systems operating in the ultra high frequency (UHF)band have a range that is typically 12 m in line of sight (LOS)conditions. This range could be drastically reduced by any blockage ofthe RFID tag or RFID reader caused by various kinds of obstacles such aspeople or furniture that results in a shadowing effect.

Because of multipath frequency selective fading, encountered in indoorenvironments, significant level variations of the received RF signal areexperienced even within a distance of a few centimeters. FIG. 5 shows agraph presenting an example of variations of magnitudes of a received RFsignal at UHF frequency within an indoor area having coordinates X and Yof 2 m×2 m, respectively. As shown in FIG. 5, variation of the RF signalof up to 40 dBm could be noticed over distances of a few tens ofcentimeters. Such fast fading signal could, disadvantageously, preventthe activation of one RFID tag even for a transmission from a close RFIDreader, situated in the same area; whereas, another RFID tag, located ina nearby area could, disadvantageously, be activated and thus read bythe RFID reader located in the area in which the one RFID tag islocated. As illustrated in the graph of FIG. 6, a situation may happenin which an RFID tag located in a so-called fade at a region 66 withrespect to a signal transmitted by an RFID reader situated in the samearea. On the other hand, an RFID tag situated a different area might belocated on a so-called crest 68.

SUMMARY

In accordance with an aspect of the disclosure, a mobile station isconfigured for performing a handoff operation in a wirelesscommunication network. It includes a radio frequency (RF) identification(RFID) transmitter for transmitting an interrogating RF signal. An RFIDreceiver stage is capable of receiving, in response to the interrogatingRF signal, a plurality of responding RF signals generated in a pluralityof RFID tags, respectively, located in a plurality of locations. Aprocessor is configured to select, in accordance with a selectioncriterion, at least one of the responding RF signals containinginformation identifying a corresponding access point (AP) and to select,in accordance with the identifying information, the identified AP from aplurality of access points (AP's) for the mobile station to associatewith in the handoff operation.

In accordance with another aspect of the disclosure, a mobile stationperforms a handoff operation in a wireless communication. It includes aradio frequency (RF) identification (RFID) transmitter for transmittingan interrogating RF signal that is applied to RFID tags arranged in RFIDtag pairs. A given RFID tag pair includes a first RFID tag and a secondRFID tag separated from each other by a distance for reducing fadingeffect. The given RFID tag pair of the RFID tag pairs is capable ofgenerating, in response to the interrogating RF signal, a firstresponding RF signal, if at all, and a second responding RF signal, ifat all, respectively. A processor is configured to select, in accordancewith a difference between a magnitude of the first responding RF signalthat is received by the processor and a magnitude of the secondresponding RF signal that is received by the processor, one of themagnitudes, when both the first and second responding RF signals aregenerated, and to select the magnitude of one responding RF signal, whenthe given RFID tag pair generates merely the one responding RF signal.The processor is additionally configured to select a location from aplurality of locations. A given location of the plurality of locationscontains a corresponding plurality of the RFID tag pairs, in a manner toreduce shadowing effect. The plurality of the RFID tag pairs containedin the given location generate at least a corresponding responding RFsignal of a plurality of responding RF signals associated with the RFIDtag pairs located in the given location. The selected location isselected in accordance with a sum of at least one selected magnitude ofa plurality of selected magnitudes associated with the plurality of RFIDtag pairs located in the selected location. The processor is furtherconfigured to select an access point (AP) from a plurality of accesspoints (AP's) for the mobile station to associate with in the handoffoperation in accordance with the selected location.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates an example of a building having, ineach location, RFID attached tag pairs, embodying a preferredembodiment;

FIG. 2 illustrates a partial block diagram of an RFID tag pair of FIG.1;

FIG. 3 illustrates a partial block diagram of a mobile device containingan RFID tag reader, embodying a preferred embodiment;

FIG. 4 illustrates a flow chart for explaining the operation of aprocessor of FIG. 3;

FIG. 5 illustrates a graph presenting an example of variations ofmagnitudes of a received RF signal; and

FIG. 6 illustrates a graph demonstrating a fading effect of a receivedRF signal.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a residential structure such as abuilding 100. Building 100 includes, for example, four locations, a Room1, a Room 2, a Room 3 and a Room 4, respectively. In each of Rooms 1 and3 in building 100 of FIG. 1, a corresponding wireless access point (AP)is installed, AP1 and AP3, respectively. Each of AP1 and AP3 allowswireless devices to connect to a network 200 using Wi-Fi, or relatedprotocols. Each AP usually connects to a router (via a wired network) asa stand-alone device, but it can also be an integral component of therouter itself.

In each room of residential building 100, for example, in Room 1, fouridentical radio frequency identification (RFID) tag sets, an RFID tagpair 11, an RFID tag pair 12, an RFID tag pair 13 and an RFID tag pair14 are installed. RFID tag pairs 11, 12, 13 and 14 are spaced apart ofeach other so as to reduce the effect of shadowing. It should beunderstood that a set may include more RFID tags than a pair. However,in the preferred embodiment each set includes just a pair of RFID tags.

RFID tag pair 11 is embedded within or rigidly attached to a region115-11 of a surface of a wall 50. Similarly, RFID tag pairs 12, 13 and14 are embedded within or rigidly attached to a region 115-12 region, aregion 115-13 and a region 115-14 of a surface of a wall 51, a ceiling52 and a flooring 53, respectively. RFID tag pairs 11, 12, 13 and 14 areassociated merely with Room 1 and with AP1 and none is associated withany other Room or with another AP. An RFID tag pair 21, an RFID tag pair22, an RFID tag pair 23 and an RFID tag pair 24 are similarly installedin room 2 and are associated with Room 2 and with AP3 and none isassociated with any other Room or with another AP. An RFID tag pair 31,an RFID tag pair 32, an RFID tag pair 33 and an RFID tag pair 34 aresimilarly installed in Room 3 and are associated with Room 3 and withAP3 and neither is associated with any other Room or with another AP.Lastly, an RFID tag pair 41, an RFID tag pair 42, an RFID tag pair 43and an RFID tag pair 44 are similarly installed in room 4 and areassociated with room 4 and with AP1 and none is associated neither withany other Room or with another AP. Being associated with a given roomindicates that the corresponding RFID tag pair is contained in the givenroom. Being associated with a given AP indicates that the correspondingAP would be the preferred AP to associate or re-associate with in ahandoff process.

Each RFID tag pair, for example, RFID tag pair 11 of FIG. 2, forms a setthat includes an RFID tag 11 a and an RFID tag 11 b, each being of thepassive type that does not require wired connection to a power supplyfor energization. Similar symbols and numerals in FIGS. 1 and 2 indicatesimilar items or functions. RFID tag 11 a, for example, of FIG. 2 ispaper thin constructed on a flexible plastic substrate 115 with adhesivefor its fixation. Substrate 115 may be optically transparent or may havethe wall/ceiling color to be visually unobtrusive. RFID tag 11 aincludes an etched directional antenna 110 having a hemispherical orhalf space radiation coverage, a tiny chip 114 which includes a memory112 for storing data and a transceiver 113 that is coupled to antenna110 in a conventional manner. The data in memory 112 may contain anidentifier, not shown, identifying the room and region in which RFID tag11 a is installed which, in this example, is room 1, region 115-11 andwall 50 of FIG. 1. It may also contain the RFID tag pair identifierwhich, in this example, identifies it as being included in RFID tag pair11 and having an identification portion that differentiates it from theother RFID tag 11 b, of the same RFID tag pair 11. In addition, it maycontain necessary information required by the protocol of Wi-Fi wirelessnetwork 200 for addressing and associating or re-associating thepreferred AP in a handoff process, which, in this example, is AP1. RFIDtag 11 b may be similarly constructed on flexible plastic substrate 115as RFID tag 11 a but is attached to wall 50 of FIG. 1 at a distance, d,from RFID tag 11 a. RFID tag 11 a and RFID tag 11 b may be substantiallyidentical except for the identifier, not shown, that differentiates RFIDtag 11 b from RFID tag 11 a.

FIG. 3 illustrates a partial block diagram of a mobile device, forexample, a smart phone 60 capable of communicating in, for example, aWi-Fi wireless network 200 via AP1 and AP3 of FIG. 1. Smart phone 60also includes an RFID tag reader 61 forming both an RF receiver and anRF transmitter, embodying an advantageous feature. Similar symbols andnumerals in FIGS. 1, 2 and 3 indicate similar items or function. Whensmart phone 60 that contains Reader 61 of FIG. 3 is carried by a user,not shown, it can be used for identifying, for example, a room fromamong rooms 1-4 of FIG. 1 where mobile smart phone 60 is located and anAP that is most appropriate for association or re-association with smartphone 60 in a handoff process, when mobile smart phone 60 is located insuch room.

RFID reader 61 of FIG. 3 includes a processor 64 which may be realizedas a digital signal processor (DSP). Processor 64 is coupled to a bus 65for coupling processor 64 to a memory 66 and to a motion detector 67such as an accelerometer. Processor 64 is coupled via an RFIDtransceiver 62 to an antenna 63.

The operation of processor 64 is explained in connection with a flowchart of FIG. 4. Similar symbols and numerals in FIGS. 1, 2, 3 and 4indicate similar items or functions. In an operation block 400 of FIG.4, processor 64 of FIG. 3 waits for a movement or motion indication, notshown, from motion detector 67. The movement indication is tested in adecision block 401 of FIG. 4 to determine whether smart phone 60including RFID tag reader 61 has been moved. When motion detector 67 isindicative of a movement of portable RFID reader 61, the result is “yes”in decision block 401 of FIG. 4. Consequently, in a block 402, processor64 of FIG. 3 is triggered to generate a transmission of an interrogationor selection RF signal 63 a that is modulated to contain an address forsequentially and selectively addressing each RFID tag, for example, RFIDtag 11 a of FIG. 2 of tag pair 11 of FIG. 1. By not initiating thecommunication unless and until motion detector 67 becomes indicative ofa movement of portable reader 61, current consumption of RFID reader 61is, advantageously, reduced in a manner to conserve a charge in abattery, not shown, of smart phone 60.

It is known to use a variety of techniques to transmit and receive datato and from the corresponding RFID tag including amplitude modulation(AM), phase modulation (PM), and frequency modulation (FM). Furthermore,the data transmitted can be encoded using any of a variety oftechniques, including frequency shift keying (FSK), pulse positionmodulation (PPM), pulse duration modulation (PDM), and amplitude shiftkeying (ASK).

In the example of FIG. 1, RFID tag 11 a of FIG. 2 is exposed to an RFfield produced by antenna 63 of FIG. 3. Consequently, it absorbs energyfrom the RF transmissions of antenna 63 of reader 61 acting astransmitter and uses the absorbed energy for energizing chip 114 of FIG.2 to perform data retrieval and data transmission. Upon decodingtransmission of interrogation or selection RF signal 63 a of FIG. 3 thattargets, for example, RFID tag 11 a, the aforementioned informationstored in memory 112 of RFID tag 11 a of FIG. 2 is transmitted byantenna 110 and, in this example, a corresponding responding RF signal111 a is received via antenna 63 of reader 61 of FIG. 3 acting as areceiver.

In an operational block 403 of FIG. 4, Processor 64 of FIG. 3 detectsresponding RF signal 111 a and stores in memory 66 a correspondingReceiver Signal Strength Indicator (RSSI) value that is indicative of amagnitude of responding RF signals 111 a received from RFID tag 11 a ofFIG. 2 of tag pair 11. In addition, processor 64 of FIG. 3 stores inmemory 66 the corresponding identifier information such as the roomnumber that, in this example, is Room 1 and information capable ofidentifying the associated AP that, in this example, AP1 is associatedwith Room 1 including addressing information. Such addressinginformation may be required by smart phone 60 for communicating with theassociated AP1 using the protocol of Wi-Fi network 200. Processor 64 ofFIG. 3 also stores in memory 66 a number identifying RFID tag 11 a andRFID tag pair 11 from the information contained in responding RF signal111 a. Similarly, RFID reader 61 of FIG. 3 communicates with RFID tag 11b of FIG. 2 and with each of the remaining RFID tags of RFID tag pairs12-14, 21-24, 31-34 and 41-44 of FIG. 1, during a sequence of timeslots, respectively, not shown. The result is that the correspondinginformation for each responding RFID signal, if any, generated in RFIDtag pairs 11-14, 21-24, 31-34 and 41-44 of FIG. 1 is stored, similarlyto that stored for responding RF signal 111 a, is stored in memory 66 ofFIG. 3.

If, in block 403, no responding RF signal is received by processor 64 ofFIG. 3 from any of the targeted RFID tags of RFID tag pairs 11-14,21-24, 31-34 and 41-44 of FIG. 1, represented by, T=0, in a decisionblock 404 of FIG. 4, processor 64 of FIG. 3 will keep sendingtransmission of interrogation, as suggested by the “yes” path ofdecision block 404. On the other hand, if at least one responding RFsignal has been received, in the aforementioned sequence of time slots,the “no” answer of decision block 404 indicates that an operation block405 will follow.

In operation block 405 of FIG. 4, processor 64 of FIG. 3 selects thelargest (or larger, in the case of a pair of responding RF signals)stored RSSI value of each set of responding RF signal pairs generated ineach responding RFID tag pair. For example, assume that a responding RFsignal 111 a of FIGS. 1 and 2 happens to have a larger RSSI value thanthat of a responding RF signal 111 b, originated in RFID tags 11 a and11 b, respectively, of FIG. 2 of RFID tag pair 11. In this case, theRSSI value of responding RF signal 111 a will be selected and stored.This would also be applicable in the special situation in which RFsignal 111 a is received but no responding RF signal 111 b is detected.As indicated before, tag pair 11 is associated with region 115-11 of aportion of wall 50 of room 1 of FIG. 1 where substrate 115 of FIG. 2 isattached. RFID tag pair 11 is also associated with AP1. Similarcommunication process is applied with respect to each of the otherresponding RF signals originated in the corresponding RFID tag pairs12-14, 21-24, 31-34 and 41-44 of FIG. 1. For example, a stored RSSIvalue associated with a larger responding RF signal 121 a of a set ofresponding RF signal pair that includes RF signal 121 a and an RF signal121 b might be selected for representing tag pair 12 in furtherprocessing steps; whereas, in this example, a stored RSSI value ofresponding RF signal 121 b will not be selected or excluded from havingany further effect. Similarly, a stored RSSI value associated with aresponding RF signal 211 a might be selected for representing tag pair21 in following processing steps; whereas, in this example, a storedRSSI value of a responding RF signal 211 b will not be selected.Likewise, a stored RSSI value associated with a responding RF signal 241a might be selected for tag pair 24; whereas, in this example, a storedRSSI value of a responding RF signal 241 b will not be selected.

Thereafter, in an operation block 406 and a decision block 407,processor 64 of FIG. 3 determines, in accordance with the informationstored in memory 66, whether each of the responding RF signals hasoriginated in a single room or associated with a single AP. In thisexample, it could be just Room 1 or AP1 of FIG. 1, respectively.

In the majority of situations, it is more likely that all responding RFsignals originate in a single room. Thus, if the answer in decisionblock 407 of FIG. 4 is “yes”, processor 64 of FIG. 3 determines, in anoperation block 410 of FIG. 4, the room in which mobile station 60 ofFIG. 3 is located. In the example of FIG. 1, processor 64 of FIG. 3determines that mobile station 60 is located in Room 1. The sameoperation also determines the AP with which mobile smart phone 60 shouldpreferably associate in a handoff process. In the example of FIG. 1,processor 64 determines that mobile smart phone 60 should preferablyassociate with AP1.

On the other hand, in rarely occurring situations, not all theresponding RF signals originate in a single room or not all theresponding RF signals are associated with a single AP, resulting in theanswer, “no”, in the aforementioned decision block 407 of FIG. 4.Therefore, an operation block 408 will follow. Thus, operation block 408follows when RFID reader 61 receives, in addition to, for example,responding RF signal 111 a that originated in Room 1 and associated withAP1 of FIG. 1, also, for example, a responding RF signal 211 a, aresponding RF signal 211 b or both. Responding RF signals 211 a and 211b have been generated in RFID tag 21 of room 2 that is outside Room 1 inwhich Mobile smart phone 60 is presently located. Similarly, respondingRF signals 211 a and 211 b, in this example, are associated with AP3located in room 3. RFID reader 61 might receive, in addition, forexample, a responding RF signal 241 a or a responding RF signal 241 boriginated from RFID tag pair 24 or both that are located in Room 2 andare also associated with AP3. As explained later on, in operation block408 and in the following operation blocks 409 and 410, using theinformation contained in or derived from the responding RF signals,processor 64 of FIG. 3 determines the room number in which smart phone60 is located and, similarly, the AP which Mobile smart phone 60 shouldpreferably select to associate with in a handoff process.

A responding RF signal originated in, for example, tag pair 21 might besubject to the aforementioned multipath frequency selective fadingproblem encountered in indoor environments. Consequenltly andcounter-intuitively, received responding RF signal 211 a that aregenerated in Room 2 and associated with AP3 might happen to be evenlarger than received responding RF signal 111 a generated in Room 1 ofFIG. 1, in which Mobile smart phone 60 is presently located, andassociated with AP1. This could have led to an identification errorresulting in a false determination. Such false determination indicates,for example, that the room in which Mobile smart phone 60 is located isroom 2 and the AP with which Mobile smart phone 60 should preferablyselect to associate would be AP3 instead of a correct determination ofAP1 of Room 1, where it is actually located. To avoid such an error, theRFID tags of each RFID tag pair, for example, RFID tags 11 a and 11 b ofthe set of RFID tag pair 11 of FIG. 2 are separated from each other bythe aforementioned distance, d.

Distance, d, is selected to be greater than a coherence distance, λ/4,associated with the frequency of the radiated RF signal which, at 900MHz, is approximately 8 cm. However, distance, d, is also selected to besmaller than λ/2 which at 900 MHz is approximately 16 cm. Becausedistance, d, is greater than the coherence distance, λ/4, it is unlikelythat, for example, both responding RFID signals 111 a and 111 bgenerated in RFID tags 11 a and 11 b, respectively, will simultaneouslyencounter the multipath frequency selective fading problem. Thus, themultipath frequency selective fading problem that may be encountered inindoor environment such as in Room 1-Room 4 of FIG. 1 is,advantageously, mitigated.

In the example referred to before, each selected responding RF signal111 a, 121 a, 211 a and 241 a that was selected on the basis of havingthe larger RSSI value of the pair of responding RF signals generated inthe corresponding RFID tag pair. In operation block 408 of FIG. 4, thestored RSSI values of all the selected larger responding RF signals fromeach tag pairs located in the corresponding room, for example, themagnitude or RSSI of each of RF signals 111 a and 121 a originated inRoom 1 of FIG. 1, are combined to form an accumulative magnitude. Thecumulative magnitude is formed by algebraically summed up RSSI ofresponding RF signals 111 a and RSSI of responding 121 a to produce afirst sum associated with Room 1. Similarly, the stored RSSI values ofeach the selected larger responding RF signals, for example, ofresponding RF signals 211 a and 241 a, originated in Room 2 are also arecombined to form an accumulative magnitude such as by beingalgebraically summed up to produce a second sum associated with Room 2.Similar operation is performed with respect to the stored RSSI values ofall selected responding RF signals, if any, associated with each ofRooms 3 and 4 that are combined to form an accumulative magnitude of athird sum, if any, and an accumulative magnitude of a fourth sum, ifany, respectively.

As shown in the example of FIG. 1, the number of RFID tag pairs in eachof Rooms 1-4 is equal to that in each of the other rooms. Accordingly,processor 64 of FIG. 3 compares the first, second, third and fourth sumsto one another for selecting the largest of the first, second, third andfourth sum, that is implemented in block 410 of FIG. 4. In block 410 ofFIG. 4, processor 64 of FIG. 3 determines, among Rooms 1-4, theparticular Room in which smart phone 60 is located by determining theroom associated with the largest of the first, second, third and fourthsums. In the same way, as explained later on in more details, processor64 of FIG. 3 determines the AP, AP1 or AP3, associated with the largestof the first, second, third and fourth sums, as being the mostappropriate AP to be selected for associating with in a handoff process.

As represented in preceding block 409 of FIG. 4, processor 64 of FIG. 3may, in addition, calculate the probability of such room as being thecorrect room to contain smart phone 60 and of such AP as being the mostpreferable one to associate with in a handoff process. This probabilityis equal to a fraction having the largest of the first, second, thirdand fourth sums, as a numerator, and a sum total of the first, second,third and fourth sums, as a denominator.

Each responding RF signal associated with the largest of the first,second, third and fourth sums may contain sufficient information to beincluded in the protocol for initiating the communication between smartphone 60 and the selected AP, AP1 or AP3 of FIG. 1, to associate withnext in a handoff operation. As an alternative, memory 66 of RFID reader61 of FIG. 3 may contain in a table, not shown, information of the AP toassociate with next when mobile station 60 is present in a given room.In the above example, the table will indicate that AP1 is theappropriate AP to associate with when RFID reader 61 of FIG. 3 islocated in either Room 1 or Room 2. In another alternative, eachresponding RF signal that originate in Room 1 or Room 2 will containsufficient information to enable the selection of AP1 as the mostappropriate AP to associate with in the handoff process.

In one embodiment, not shown, for each room in which Mobile smart phone60 is located, the user can cause smart phone 60 to store in memory 66information sufficient for enabling smart phone 60 to initiate Wi-Ficommunication with the corresponding one AP, AP1 or AP3, of FIG. 1 whichis the preferred AP to associate with next. For example, in a set-up orlearning mode of operation, that can be initiated in response to a usercommand or automatically, smart phone 60 can determine by trial anderror for a given room, in which Mobile smart phone 60 is located, theinformation required by smart phone 60 to initiate Wi-Fi communicationwith the applicable AP, AP1 or AP3, of FIG. 1 to associate with next.This information is then stored in a local table, not shown, that iscontained in, for example, memory 66 for future operations.

Following operation box 410 of FIG. 4, when the determination of thenext AP to associate with in a handoff operation has already beenaccomplished, smart phone 60 of FIG. 1 continues the handoff process innetwork 200 of an operation block 411 of FIG. 4.

Assume, for example, that smart phone 60 moves from Room 1, of FIG. 1 inwhich AP1 is the preferable AP to associate with, to Room 2, in whichAP3 located in Room 3 is the preferable AP to associate with. Forcompleting the handoff process, in order to verify that theaforementioned RFID-probe-response corresponds to AP3 of FIG. 1, mobilesmart phone 60 of FIG. 3—can broadcast in Wi-Fi network 200 aNew-AP-probe-request addressed to the next AP, AP3, of FIG. 1, in amanner similar to that defined in the IEEE 802.11 (WiFi) handoffprocess. Thus, the aforementioned RFID-probe-response will terminatewhen mobile smart phone 60 of FIG. 3 receives the New-AP-prove-responsefrom AP3 of FIG. 1, in this example. Thereafter, the AuthenticationPhase defined in, for example, the IEEE 802.11 (WiFi) handoff process,will follow in a conventional manner. This phase involves the requestand transfer of credentials and other state information from AP3 of FIG.1 to mobile smart phone 60 of FIG. 3. After successfully receiving fromAP3 of FIG. 1 the credentials and state information, mobile smart phone60 of FIG. 3 sends a Re-association Request message to AP3 of FIG. 1,which, in turn, sends a Move Request message to the previous AP which,in this example, is AP1. Then, in a conventional manner, AP3 completesthe handoff process by sending a Reassociation Response message tomobile smart phone 60 of FIG. 3.

Assume that the number of RFID tag pairs in different rooms of Rooms 1-4of FIG. 1 is unequal in a manner not shown in FIG. 1. Accordingly,processor 64 of FIG. 3 divides each of the first, second, third andfourth sums or accumulative magnitudes by the number of RFID tag pairsin Rooms 1, 2, 3 and 4, respectively, to produce a first average value,a second average value, a third average value and a fourth average valueassociated with the responding RF signals originated in Rooms 1, 2, 3and 4, respectively. Processor 64 of FIG. 3 compares the first, second,third and fourth average values to one another for selecting the largestof the first, second, third and fourth average values. The AP which isthe most appropriate one to associate with in a handoff process would bethe AP associated with the largest of the first, second, third andfourth aveage values. Similarly, the room in which mobile station 60 islocated would be associated with the largest of the first, second, thirdand fourth average values.

In addition, processor 64 calculates in an operation block 409 of FIG. 4the probability, P_(k), that such AP is the most appropriate one toassociate with in a handoff process and that such room is the room inwhich mobile station 60 is located. This is performed by calculating afraction having the largest of the first, second, third and fourthaverage values, as a numerator, and a sum total of the first, second,third and fourth average values, as a denominator.

Let S_(ij) be defined as the Maximum RSSI from a tag pair number j inroom number i. Room number i assumes the value 1, 2, . . . or R, suchthat “R” is also the total number of rooms. Tag pair number j assumesthe values 1, 2, 3, . . . or T, such that “T_(i)” is also the totalnumber of tagged pairs in room i.

-   -   1. In case where all the rooms have the same number of tag        pairs, for all i's T_(i) is equal to T.        For each room k, RFID reader 61 of FIG. 3 calculates, a sum        S_(k) of all Maximum RSSI obtained from the tag pairs situated        in a room k. Let S_(kj) be defined as the Maximum RSSI of tag        pair number j in room k. It follows that S_(k)=Σ_(j)S_(kj); j=1,        . . . , T. Thus, the room where RFID reader 61 of FIG. 3 is most        likely to be located is the room number for which the highest        value S_(k) is obtained. Also, the probability P_(k) that the        user is located in room k could be estimated as P_(k)=S_(k)/S        where S is the sum total of all the S_(k)'s or S=Σ_(k)S_(k).        Similarly, the AP which Mobile smart phone 60 should preferably        select to associate with is the AP associated with the RFID tags        of room k for which the highest value S_(k) is obtained.    -   2. In case where the number of tag pairs is not the same in all        the rooms, T_(k) represent the number of tag pairs in a room k.        For each room k, RFID reader 61 of FIG. 3 calculates the average        value of the Maximum of RSSI from tag pairs j situated in room        k, denoted as Sav_(k). Thus, Sav_(k)=S_(k)/T_(k); with        S_(k)=Σ_(j)S_(kj); j=1, 2, . . . , T_(k).

The room where RFID reader 61 of FIG. 3 is located is the room numberfor which the highest value of Sav_(k) is obtained. The probability,P_(k), that the user is located in room k could be estimated asP_(k)=Sav_(k)/Sav, where Sav is the sum of all Sav_(k) orSav=Σ_(k)Sav_(k); k=1, 2, . . . , R. Similarly, the AP which Mobilesmart phone 60 should preferably select to associate with is the APassociated with the RFID tags of room k for which the highest valueSav_(k) is obtained.

1. A mobile station configured for performing a handoff operation in awireless communication network, comprising: a long range RFIDtransmitter for transmitting an interrogating RF signal; an RFIDreceiver stage capable of receiving, in response to said interrogatingRF signal, a plurality of responding RF signals generated in a pluralityof RFID tags, respectively, located in a plurality of locations, eachresponding RF signal containing information identifying a location of aRFID tag having generated the responding RF signal; and a processorconfigured to select, in accordance with a selection criterion, at leastone of said responding RF signals containing further informationidentifying a corresponding access point, and to select, in accordancewith said identifying information, said identified access point from aplurality of access points for said mobile station to associate with insaid handoff operation.
 2. The mobile station according to claim 1,wherein said processor is configured to select said one of saidresponding RF signals (121 a), in accordance with signal strength. 3.The mobile station according to claim 1, wherein said furtherinformation contained in said selected responding RF signal thatassociates said selected responding RF signal with said selected accesspoint is capable of being used by said mobile station in a protocol ofsaid wireless communication network for performing the handoffoperation.
 4. The mobile station according to claim 1, wherein theplurality of responding RF signals include a first plurality of setsassociated with a first location of said plurality of locations and asecond plurality of sets associated with a second location of saidplurality of locations, each set of RF signals being generated by agiven RFID tag pair including a first RFID tag and a second RFID tagseparated from each other by a distance, said processor being furtherconfigured to select, in accordance with the selection criterion, afirst and a second magnitudes respectively of a first and a secondresponding RF signals in respectively a first and a second sets of saidfirst plurality of sets, said processor being configured to combine saidselected first and second magnitudes of said first plurality of sets,said processor being further configured to select, in accordance withthe selection criterion, a further first and a further second magnitudesrespectively of a further first and a further second responding RFsignals in respectively a first and a second sets of said secondplurality of sets, said processor being configured to combine saidselected further first and further second magnitudes of said secondplurality of sets, said processor being additionally configured tocompare a value indicative of said combined first and second magnitudesof said first plurality of sets with a further value indicative of saidcombined further first and further second magnitudes of said secondplurality of sets for selecting, in accordance with the comparison, thelocation corresponding to the selected at least one of said respondingRF signals.
 5. (canceled)
 6. The mobile station according to claim 4,wherein said selected location is selected in accordance with a sum ofeach selected magnitude associated with a corresponding RFID tag pair ofa plurality of RFID tag pairs that are located in said selectedlocation.
 7. The mobile station according to claim 6, wherein saidselected location is selected in accordance with said sum that is largerthan each other sum, similarly obtained, that is associated with each ofthe other locations of said plurality of locations.
 8. The mobilestation according to claim 4 wherein said mobile station is configuredto apply a protocol applicable to said selected access point inaccordance with information contained in at least a responding RF signalgenerated in a corresponding RFID tag pair located in said selectedlocation.
 9. The mobile station according to claim 4, further comprisinga motion detector wherein said RFID transmitter is responsive to anoutput of said motion detector for transmitting said interrogating RFsignal after said motion detector detects a motion of said mobilestation.
 10. The mobile station according to claim 4, wherein each ofsaid RFID tag pairs is attached to a corresponding region of a pluralityof regions of said given location, respectively.
 11. The mobile stationaccording to claim 4, wherein said distance is larger than or equal toλ/4 and smaller than or equal to λ/2 based on a frequency of aresponding RF signal of said plurality of responding RF signalsgenerated in said given RFID tag pair.
 12. An RFID tag configured fortransmitting a RFID signal in response to an interrogating RF signalaccording to claim 1, the RFID signal containing information identifyinga location of the RFID tag, the RFID signal further containing furtherinformation identifying an access point for being selected among aplurality of access points, by a mobile station to associate with in ahandoff operation.
 13. A pair of RFID tags comprising a first RFID tag,and a second RFID tag, the first and the second RFID tags beingaccording to claim 11, and being further separated from each other by adistance.
 14. The pair of RFID tags, according to claim 12, wherein saiddistance is larger than or equal to λ/4 and smaller than or equal to λ/2based on a frequency of the RF signal generated in response to theinterrogating RF signal.
 15. A computer-readable storage medium storingcomputer-executable program instructions to enable a computer to:transmit by a long-range RFID transmitter an interrogating RF signal;receive, in response to said interrogating RF signal, a plurality ofresponding RF signals generated in a plurality of RFID tags,respectively, located in a plurality of locations, each responding RFsignal containing information identifying a location of a RFID taghaving generated the responding RF signal; and select, in accordancewith a selection criterion, at least one of said responding RF signalscontaining further information identifying a corresponding access point,and to select, in accordance with said identifying information, saididentified access point from a plurality of access points for saidmobile station to associate with in said handoff operation.